1. Field of the Invention
The present invention relates to a method and an apparatus for preventing snow from melting and for packing snow in an indoor or outdoor artificial ski facility for skiing or snow-boarding.
2. Description of Related Art
In order to prevent snow from melting in an artificial ski facility, various methods have been disclosed in publications such as Japanese Patent Laid-Open No. 1-293887/1989, the related art (1); Japanese Patent Laid-Open No. 3-28405/1991, the related art (2); Japanese Patent Laid-Open No. 3-166404/1991, the related art (3); Japanese Patent Laid-Open No. 3-180604/1991, the related art (4); Japanese Patent Laid-Open No. 2-240304/1990, the related art (5); and Japanese Patent Laid-Open No. 3-93905/1991, the related art (6).
JP 1-293887/1989 discloses a method for preventing a snow cover on a platform from melting by circulating a refrigerant through cooling pipes embedded in the platform.
JP 3-28405/1991 discloses a method for preventing a snow cover on a platform from melting by transferring heat from a heat-pipe evaporator embedded directly below the surface of the platform to a heat-pipe condenser disposed on the ground such that heat around the evaporator is absorbed when the ambient air temperature drops below that of the platform.
JP 3-166404/1991 discloses a method for preventing a snow cover on a platform from melting by covering the top surface of the platform with a water-permeable thermal insulator covered with a non-woven synthetic fabric.
JP 3-180604/1991 discloses a method for preventing a snow cover on a platform from melting by covering the top surface of the platform with a snow-support sheet comprising a textile base sheet with a plastic foam thermal insulator formed on the underside thereof.
JP 2-240304/1990 discloses a method for preventing a snow cover on a platform from melting by accommodating thermal insulating members in frameworks arrayed in a lattice on the platform.
JP 3-93905/1991 discloses a method for preventing a snow cover on a platform from melting by forming a thermal insulating layer in a waterproof membrane on the platform, by constructing a retaining plate in a waterproof membrane on the heat insulating layer, and by forming a drainage channel on the retaining plate.
In these known methods, if the ambient temperature in an artificial ski facility is below 0.degree. C., since thermal transfer from the top surface of the snow is relatively small, preventing the snow from melting is possible to some extent by using some means to insulate against thermal transfer from the ground.
However, when the ambient temperature in an artificial ski facility exceeds 0.degree. C. and radiant heat is substantial as well, the above disclosed related arts (1) to (6) have problems as described below.
In the methods in JP 1-293887/1989 and JP 3-28405/1991, only the snow around the cooling pipes is cooled and the cooling efficiency of the snow at a distance from the cooling pipes is low because of high thermal insulation of snow with interstitial spaces. The surface snow layers, especially where sensible heat and radiant heat penetrate, cannot be prevented from melting.
In the methods in which a thermal insulating sheet or a thermal insulating material is disposed at the bottom of the snow or on the platform, as in JP 3-166404/1991, JP 3-180604/1991, JP 2-240304/1990 and JP 3-93905/1991, although insulation against thermal transfer from the ground is to some extent possible, insulation against thermal transfer from the top surface of the snow is impossible and fails to prevent the snow at the surface layers from melting.
In the methods in JP 1-293887/1989 and JP 3-280405/1991, there is also the following problem. As melted snow penetrates from a surface snow layer to a lower snow layer due to gravity and freezes into ice around the cooling pipes, the ice gradually grows into a frozen mass at the bottom of the snow cover due to the inflow of the melted snow, and this continues growing toward the surface snow layer until finally almost all the snow cover is converted into a frozen ski slope. Such a frozen ski slope is so hard that it results in disadvantages such as difficulty in riding on edges of skis, which may easily cause falling, requiring substantial time for slope maintenance, and difficulty in applying new snow due to the impossibility of replacement.
The method in JP 3-166404/1991 also has a problem in that with an increase in the ambient temperature, the rate of snow melting increases so much that hardness and shearing strength of the snow are significantly reduced. This results in decreasing of the suitability of the slope for skiing.